1. Field of the Invention
The present invention relates to a technology for implementing rattling prevention of a control unit, which is to be mounted on a vehicle or the like.
2. Description of Related Art
As a structure for preventing rattling and abnormal noise etc. caused thereby in a storage case for storing a control unit for a power steering or the like in a vehicle, for example, the ones described in Patent Document 1 or Patent Document 2 are known.
In other words, the structure in Patent Document 1 is a part storage case of a structure including an inner plate and an outer plate provided on a base, a peripheral wall of a bottomless box-shaped cover inserted between the inner plate and the outer plate, a window provided on the peripheral wall of the cover, an outward projection to be fitted to the window on the inner plate, an inward projection for pressing the peripheral wall inward on the outer plate, wherein only upper and lower bevels of the outer projection come into sliding contact with the upper and lower sides of the window.
In Patent Document 2, there is described a fitting structure between a case and a lid including: a guide (flange) provided on a plate-shaped lid to be fitted to an opening of a box-shaped case; the guide coming into abutment with an inner wall near an end edge of the opening of the case; the lid being fitted to the case along the guide, wherein a surface of the guide which comes into abutment with a corner of the end edge of the opening of the case is formed with a tapered rib so as to project therefrom and incline toward the plate-shaped lid from the guide, the case is formed with a thinned portion having a reduced thickness at a position corresponding to the rib, and the thinned portion climbs over the rib and hence is deformed when the case and the lid are fitted.
Patent Document 2 also describes a fitting structure between a case and a lid including: a guide (flange) provided on a plate-shaped lid to be fitted to an opening of a box-shaped case; the guide coming into abutment with an inner wall near an end edge of the opening of the case; the lid being fitted to the case along the guide, wherein a surface of the guide which comes into abutment with a corner of the end edge of the opening of the case is formed with a tapered rib formed of resin contained material so as to project therefrom and incline toward the plate-shaped lid from the guide, and the corner of the end edge of the opening of the case is adapted to chip the rib away when the case and the lid are fitted. In this structure, it is also described that the lid further includes a recess in the vicinity of the rib for storing chips generated by the corner of the end edge of the opening of the case.
[Patent Document 1] JP-A-9-181461
[Patent Document 2] Japanese Patent No. 2978120
However, the storage case in the related art described above has a following problem to be solved. In the structure of Patent Document 1, it is necessary to increase the dimensional accuracy of the base or the like significantly in order to prevent rattling, and hence it is eventually difficult to prevent rattling.
The reason is as follows. In order to prevent rattling in the structure disclosed in Patent Document 1, it is necessary to achieve a clamping state in which the peripheral wall of the cover is clamped by a certain extent of pressure between the inner plate and the outer plate (the inward projection of the outer plate presses the peripheral wall of the cover and the upper and lower bevels of the outward projection of the inner plate are in press contact with the upper and lower sides of the window of the peripheral wall of the cover), that is, a state in which a reaction force from the peripheral wall of the cover is exerted to the inner plate and the outer plate, and hence they are resiliently deformed inwardly and outwardly. However, since the inner plate and the outer plate are members which are provided on the base so as to project therefrom (provided in substantially upright posture) and are short in the vertical direction, the displaceable amount which can be resiliently deformed is small. Therefore, when the margin of error in dimension of the inner plate or the outer plate, or in thickness of the peripheral wall of the cover, etc. is large, it is highly likely that the inner plate or the outer plate is deformed beyond the resiliently deformable limit depending on the cases, and hence the inner plate or the outer plate becomes damaged or is resulted in plastic deformation (permanent deformation), which may lead malfunction of the clamping state and thus rattling. Alternatively, in contrast to it, it is highly likely that a clearance is generated between the peripheral wall of the cover and the respective plates due to the dimensional error and hence the clamping state cannot be achieved at the time of assembly, and abnormal noise or cracks, etc. due to rattling are resulted.
In particular, when the base is formed of metal such as aluminum casting and the cover is formed by pressing a steel plate in order to efficiently release heat generated by a stored electric circuit outward, it is difficult to improve the dimensional accuracy of the inner plate, the outer plate, or the peripheral wall of the cover, and hence the above-described problem can easily be generated. When the base or the cover is formed of metal as described above, a large noise or abnormal vibrations may easily be generated due to rattling. However, with the structure disclosed in Patent Document 1, such problems cannot be solved easily and sufficiently from the reasons described above.
In Patent Document 1, when the peripheral wall of the cover is inserted between the inner plate and the outer plate, the inward projection of the outer plate and the peripheral wall of the cover, and the outward projection of the inner plate and the peripheral wall of the cover come into slide contact with each other (it is not possible to assemble without sliding contact). Therefore, there arises a problem such that generation of the chips due to sliding contact cannot be avoided. The chips may cause malfunction or short-circuit and hence burning of the stored electric circuit particularly when they are formed of metal. Therefore, in the case of the vehicle-mounted equipment which requires reliability, generation of such chips is not accepted.
The structure of Patent Document 2 is a structure in which the end edge (thinned portion) of the opening of the case climbs over the rib formed on the guide of the lid and hence is deformed when the case and the lid are fitted together, or a structure in which the corner of the end edge of the opening of the case chips the rib formed of resin contained material away. Therefore, the chips are inevitably generated or the probability of generation of the chips is significantly high, and hence it cannot be applied to the vehicle-mounted equipment. Although there is a description in Patent Document 2 such that the recess is formed in the vicinity of the rib of the lid to store the chips generated by the corner of the end edge of the opening of the case, there is no guarantee that the chips do not enter into the interior of the storage case (for example, on the electric circuit therein), and as long as the chips are generated, it is difficult to apply this structure to the vehicle-mounted equipment which requires reliability.
In the case of the latter structure in Patent Document 2 (the structure in which the rib of resin contained material is provided), if the case or the lid is formed of metal as described above, it is necessary to form only the rib portion of resin contained material, and hence the manufacturing cost may increase.